title: DFT calculations and electronic absorption spectra of some, α- and γ-pyrone derivatives.
abstract: The electronic absorption spectra of 6-ethyl-4-hydroxy-2,5-dioxo-pyrano[3,2-c] quinoline 1, 6-ethyl-4-hydroxy-3-nitro-2,5-dioxo-pyrano[3,2-c] quinoline 2, 6-ethyl-4-chloro-2,5-dioxo-pyrano[3,2-c] quinoline 3, 6-ethyl-3-nitro-4-chloro-2,5-dioxo-pyrano[3,2-c] quinoline 4, 6-ethyl-4,5-dioxopyrano[3,2-c] quinoline 5, and 6-ethyl-3-nitro-6H-pyrano [3,2-c]quinoline-4,5-dione 6, were measured in polar (methanol) as well as nonpolar (dioxane) solvents. The geometries were optimized using B3LYB/6-311G (p,d) method. The most stable geometry of the studied compounds, 1-6, is the planar structure as indicates by the values of the dihedral angles. The insertion of a nitro group in position 3 in both α- and γ-pyrone ring decreases the energy gap and hence increases the reactivity of 3 and 6 compounds. Assignment of the observed bands as localized, delocalized and/or of charge transfer (CT) has been facilitated by TD-DFT calculations. The correspondences between the calculated and experimental transition energies are satisfactory. The solvent and substituent effects have been investigated. Chloro-substituent has a higher band position and intensity effects on the spectra more than hydroxyl or nitro groups.
authors.affiliation: Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt.
authors.forename: Walid M I
authors.initials: WM
authors.lastname: Hassan
authors.forename: Hussein
authors.initials: H
authors.lastname: Moustafa
authors.forename: Mohamed N H
authors.initials: MN
authors.lastname: Hamed
authors.forename: Laila I
authors.initials: LI
authors.lastname: Ali
authors.forename: Shimaa Abdel
authors.initials: SA
authors.lastname: Halim
mesh_terms: D000042:Absorption; D004583:Electrons; D008958:Models, Molecular; D011753:Pyrones / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011753:Pyrones; D012997:Solvents
keywords: Alpha and gamma pyrone derivatives; MO-calculations; Solvent effect; TD-DFT; UV spectra